Two main types of ancient Greek philological annotations can be distinguished: signs and explicit notes. The first philological sign (σημεῖον) invented by the first head of the Alexandrinian Library, Zenodotos of Ephesos, in his edition of Homer has been the Obelos (ὀβελός: -), a short horizontal dash, which Zenodotos used to mark spurious lines. For this reason, the practice of using signs for textual criticism has been called 'Obelism'. Aristophanes of Byzantium invented later the asterisk (ἀστερίσκος: *) to mark lines, that are duplicated from another place as well as the Lunate Sigma (σίγμα: Ϲ) and the antisigma (ἀντίσιγμα: Ͻ) for two consecutive and interchangeable lines of the same content. A system of dots also credited to Aristophanes of Byzantium was developed in the 3rd century BC: a low dot ⟨.⟩ marked an occasion for a short breath after a short phrase, a middot (στιγμή) ⟨·⟩ marked an occasion for a longer breath after a longer passage, and a high dot ⟨˙⟩ marked a full stop at the end of a completed thought. Other writers employed two dot punctuation ⟨⁚⟩ to mark the ends of sentences or changing speakers. Less often, arrangements of three ⟨⁝⟩, four ⟨⁞⟩ and ⟨⁘⟩, and five dots ⟨⁙⟩ appeared.
The number of the philological signs and in some cases their meanings were modified by Aristarchos of Samothrake (220–143 BC), sixth head of the Alexandrinian Library. He used critical and exegetical signs in his editions of the Homeric poems. A dotted lunate sigma (σίγμα περιεστιγμένον: Ͼ) was used by him as an editorial sign indicating that the line so marked is at an incorrect position. Similarly, an antisigma, or reversed sigma (Ͻ), may mark a line that is out of place. A dotted antisigma or dotted reversed sigma (ἀντίσιγμα περιεστιγμένον: Ͽ) may indicate a line after which rearrangements should be made, or to variant readings of uncertain priority. The Diple marked lines, whose language or content was perhaps also exegetically noteworthy and pointed to a corresponding explanation in a commentary. The diple periestigmene (διπλῆ περιεστιγμένη) a dotted Diple to point to a verse in which Aristarchos' text differs from that of Zenodotos. He used the obelos added to the asteriskos (*-) where the repeated line is out of place and the stigme (στιγμή: ·) indicated suspected spuriousness.
Aristarchos' semeia became the standard philological signs for centuries to follow, also adopted early on by scholars in Rome. Some papyrus fragments contain un-Aristarchian signs whose use was fairly consistent nevertheless. For instance, the so-called ancora, an anchor-shaped diagonal upward and downward pointer often marks places were text had been omitted or draws attention to text-critical restoration in the top or bottom margin. The Hypodiastole, a curved interpunct was used to disambiguate certain homonyms and showed also that a series of letters should be understood as two separate words. Its companion mark was the enotikon (ἐνωτικόν: ‿) served to show that a series of letters should be read as a single word. The Paragraphos marked a division in a text. The Coronis was used to mark the ends of entire works or major sections in poetic and prose texts.
- Brill's Companion to Ancient Greek Scholarship, 2015 (2 Vols.) pp. 549-562 and The ambiguity of signs: critical σημεῖα from Zenodotus to Origen Author: Francesca Schironi
- Nicolas, Nick (2005). "Greek Unicode Issues: Punctuation". Thesaurus Linguae Graecae. University of California, Irvine. Archived from the original on 2014-10-10. Retrieved 2014-10-07.
- Paul D. Wegner (2006). A student's guide to textual criticism of the Bible. InterVarsity Press. p. 194. ISBN 978-0-19-814747-3.
- George Maximilian Anthony Grube (1965). The Greek and Roman critics. Hackett Publishing. p. 128. ISBN 978-0-87220-310-5.